Capacity extension is required in an existing optical network in order to provide various multimedia services such as a gradually increased data traffic, a high definition television (HDTV), electronic commerce, and video on demand (VOD), etc. For this purpose, a study on optical fiber based PON technologies has attracted considerable attention. A wavelength-division multiplexing (WDM) technology among current PON technologies is perceived to be an ultimate alternative. In the WDM technology, one wavelength per subscriber must be assigned to provide virtual point to point connectivity. Thus, it is essential in the WDM-PON technology to embody a low-cost light source for subscribers.
A wavelength locked FP-LD is recently suggested and recognized as an economic light source for WDM-PON (See Korean Patent No. 325687 registered on Feb. 28, 2002 entitled “A low-cost WDM source with an incoherent light injected Fabry-Perot semiconductor laser diode” by the inventors Chang-Hee, Lee and Hyun-Deok, Kim). Here, the wavelength locked FP-LD is a light source which is obtained by injecting a filtered incoherent light source or a BLS into an FP-LD oscillating in a multi-mode and locking the oscillating wavelength of the FP-LD to the wavelength of the injected BLS so as for the FP-LD to oscillate in a single mode.
Here, a BLS to be injected for locking wavelength may be a light emission diode (LED), erbium-doped fiber amplifiers (EDFA) emitting amplified spontaneous emission (ASE), a super luminescent diode (SLD), etc. (See T. W. Oh, et al., “Broadband Light Source for Wavelength-Division Multiple Access Passive Optical” OECC, 2003). However, the main disadvantage for LED, EDFA, and SLD, etc. is a large size or high cost. Unlike them, a BLS using mutual injection of FP-LDs is compact and possible to embody at a low cost and thus is more advantageous in implementing an economic WDM-PON (See K. M. Choi, et al., “Broadband Light Source by Mutually Injected FP-LDs” OECC, 2004).